Pyrotechnics can be grouped into at least six families: decoy flares, illuminating flares, colored flares, smokes, igniters/starters and miscellaneous pyrotechnic items. Decoy flares include infrared (IR) and solid pyrophoric flares. Aircraft pyrophoric decoy flares are typically solid pyrotechnic devices ejected as a precautionary measure or in response to a missile warning system. The most significant requirement of the device is that it develops a high-intensity, characteristic signature rapidly. In order to meet this requirement, the energy radiated by the flare is typically provided by a pyrotechnic reaction. Pyrotechnic compositions have been shown to provide high energy densities and reasonable storage life at moderate cost. The most common composition of a typical pyrotechnic flare consists of pyrophoric iron. This composition provides the high energy density desired for the decoy and also produces solid combustion products for good radiation efficiency. The net reaction of these flares is shown in Equation 1:2Fe(s)+3/2O2→Fe2O3(s)+heat  Equation 1
Decoy materials of this composition undergo the above reaction to reach temperatures of about 820° C. in less than about one second and above about 750° C. for about twelve seconds after their exposure to air. The thermal response can be increased or decreased with the addition of metals that undergo very exothermic reactions when heated in air (e.g., B, Al, Zr, Ti, etc.) or inert metal oxides (e.g., SiO2, Al2O3, etc.), respectively.
A typical pyrophoric decoy flare is composed of pyrophoric iron coated onto steel foil. The pyrophoric iron coating is usually prepared by mixing Fe and Al powders in a slurry containing a suitable solvent and binder. A very thin steel foil is then coated with the slurry by either dip coating or spraying. The resulting material is then rapidly heated to 500° C. to drive off the solvent and binder to yield a coating of the metallic powders. The coated substrate is then heated to relatively high temperatures (about 800° C.-1000° C.) in both H2 and Ar atmospheres to from an iron/aluminum alloy. The resulting alloy can be leached with a hot (about 100° F.-200° F.) caustic aqueous solution of about 10-20% sodium hydroxide (by mass) to leach the aluminum from the alloy and render the remaining iron porous and highly pyrophoric. Some prior processes claim that use of stannite (dissolved as SnCl2 or Sn(s)) in the aqueous leaching solution increases the activity (i.e., makes the iron more pyrophoric) and the lifetime of the active decoy. There are several variations of the described manufacturing technique that allow the preparation of the pyrophoric iron as a powder or a coating on a metal foil. Pyrophoric foils are particularly attractive for their ability to be dispersed from the aircraft in a cloud-like pattern. The high surface area to mass ratio of the foils causes them to flutter after being ejected from the aircraft and take on the appearance of a moving hot cloud when several decoys are ejected in rapid succession. This signal is attractive to the IR-seeking missile. Current pyrophoric decoy composition and performance can be modified through manipulation of the manufacturing process.
Having a small amount of a substance in intimate contact with the pyrophoric iron that undergoes an exothermic reaction when heated can increase the pyrophoric action of the decoy flare material. Metals, such as boron or titanium, can be added to the pyrophoric foils to achieve this desired result. Alternatively, the pyrophoric iron can be coated with aqueous solutions of commercially available alumina or silica sol that coat the porous base metal. The inert oxide coating blocks O2 from getting to the iron too rapidly and hence slows down the burn rate and makes the pyrophoric response of the material less intense. The pyrophoric iron generated by the above processes can be stored in solvents such as acetone, ethanol, and methanol, under certain conditions, with little loss in their pyrophoric performance. The current process relies heavily upon the use of hot caustic leaching solutions to prepare the high surface area porous pyrophoric Fe metal. These solutions are corrosive and represent both a safety and environmental hazard.
Production of pyrophoric iron in a simple and safe manner would be advantageous from a safety and environmental point of view. Therefore, it would be desirable to achieve pyrophoric activity in a material that is safer to process and more environmentally friendly, while still achieving similar pyrophoric activity as is seen in pyrophoric iron produced via conventional techniques.